Former U.S. Ambassador Thomas Schweich was seriously exploring a primary challenge to Republican Roy Blunt in the Missouri Senate race -- and won some high-profile support -- but announced today that he’s not running and is endorsing Blunt:

A few weeks ago, I stated that I was considering running for the U.S. Senate seat being vacated by Sen. Kit Bond. At that time, I indicated that I would only run if my candidacy would contribute to party unity and would make it more likely that Republicans keep the Senate seat. Since that time, I have met Republicans throughout the state to discuss the Senate race. These conversations were very helpful to me.

However, as a result of these discussions, I have concluded that my entering the race would be divisive and probably lower the chances of keeping Sen. Bond's seat in Republican hands. I have also had the chance to speak with Rep. Roy Blunt, and he has addressed in a forthright and admirable way the issues that I and others have previously raised about his candidacy. As a result, in the name of party unity, I have chosen not to run for U.S. Senate. I believe that we should unite behind Rep. Blunt."

Schweich's comments are a notable shift from his posture just last month, when he called Blunt virtually unelectable and unfavorably described him as a Washington insider.